Study of Magnetic Materials by Mössbauer Thermal Scans. Application to Nanocrystalline Systems

F.H. SÁNCHEZ; G.A. PASQUEVICH; P. MENDOZA ZÉLIS; A.F. CABRERA; L. YING-FENG; M. VÁZQUEZ

JOURNAL OF METASTABLE AND NANOCRYSTALLINE MATERIALS

Año: 2004 vol. 22 p. 39 - 44

1422-6375

Mössbauer thermal scans (2 K/min) have been applied to the classical amorphousfinemet-type precursor Fe73.5Si13.5Nb6Cu1B9 alloy. They allowed the determination of the orderingtemperatures of the amorphous phase before (TC = 624 K) and after partial (TC = 674 K) andcomplete (TC = 595 K) crystallization. The existence of three well differentiated temperatureregions is observed, corresponding to the ferro to paramagnetic transition of the amorphous,nanocrystallization of bcc Fe(Si) and the ferro to superpara or paramagnetic transition of thecrystalline phase. The crystallization kinetics at 763 K and 805 K was studied by two differentapproaches. At 763 K spectra were recorded every two hours up to a total time of 117 h. At 805 Kscans were used due to the much higher transformation rate. Both results were analized withtheoretical contributions representing the amorphous, very small crystals or embryos and grown upcrystals. The evolution of their relative abundances obtained with the two approaches wasconsistent. The embryo nucleation was almost completed after two and eight hours at 763 and 805K, respectively.